Actuator and a bow

ABSTRACT

A pneumatic actuator having therein a venting element and a porous element, compression and elongation of the actuator creating an air flow in the venting element and porous element to output lubricant as a mist toward a sliding interface of the actuator. A bow using the actuator and a bow having a double string preventing sideward movement when launching an arrow. A compound bow having limbs with multiple rotatable elements and an actuator rotating such elements to launch an arrow.

CROSS REFERENCE TO RELATED APPLICATIONS

The instant application is a continuation application of and claimspriority to U.S. application Ser. No. 17/289,120, filed on Apr. 27,2021, which is a U.S. National Stage application of and claims priorityto PCT/EP2019/078081, filed on Oct. 16, 2019, which is a PCT applicationof and claims priority to DK Application No. PA 2018 70705, filed onOct. 31, 2018, the subject matter of all aforementioned applications arehereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a pneumatic actuator and/or a bow andin particular to improvements of bows. One embodiment is a bow with thepneumatic actuator which increases the range of the arrow as well as thevelocity and thus precision thereof. Another situation relates to a bowwith a double string reducing undesired movement of the arrow during andafter launch. Yet other situations relate to improved compound bows.

BACKGROUND

It is often desired that bows launch arrows/bolts with as high avelocity as possible, as this increases the accuracy of the bow.

Bows are described in e.g. U.S. Pat. Nos. 3,486,495, 9,255,753,8,136,514, US2005123883, U.S. Pat. Nos. 5,445,139 and 6,253,752.

SUMMARY

The present invention addresses many obstacles present in the knowntechnology. The present bow may increase the accuracy of arrows in anumber of ways.

In a first aspect the present invention relates to a pneumatic actuatorcomprising:

a first portion and a second portion, the first portion defining aclosed channel, the second portion having a part being slidablypositioned in the channel, the part having an end portion positioned inthe channel, the first and second portions defining an elongatecompartment comprising at least a portion of the channel;

-   a lubricating element provided in the compartment, the lubricating    element having:    -   a first surface facing the first portion,    -   a second surface facing the second portion,    -   one or more channels extending from the first surface to the        second surface and    -   a lubricant in or on the lubricating element.

In the present context, an actuator is an element configured to exert aforce to an element or between elements connected thereto. In apreferred embodiment, the actuator is compressible, bendable orextendable to bias the actuator, for the actuator to subsequently beable to exert an oppositely directed force between elements connectedthereto.

The actuator may be manually energized or tensioned so that the actuatormay be used without any other power source.

The first portion defines a closed channel. Preferably, the channel isclosed at one end by the first portion and at the other end by thesecond portion. The channel may have the same cross section along atleast a portion of its length, such as a portion thereof engaged orengageable by the second portion.

Alternatively, the second portion may have an outer side with the samecross section for a length thereof introducible into the first channel,so that a part of the first portion engaging the second portion may forma sealed connection while the second element is translated into and outof the first channel.

The second portion may travel inside the channel as a piston in acylinder.

The end portion of the second portion may be the portion of the secondportion extending the farthest into the channel. The end portion may beengaging the channel and thus form a seal between the channel wall andthe second portion.

A sealing element may be provided between the first and second portions,or the end portion may perform this sealing, so that the compartment isair tight or at least substantially air tight. Then, a reduction in thevolume of the compartment will increase an air pressure in thecompartment acting to force the second portion outwardly of the channelagain. Naturally, the degree of sealing will depend on the use of theactuator.

In fact, the actuator may have, even in its most expanded state, apressure exceeding 1 atm therein, such as a pressure of 20 bar or more,such as 40 bar or more, such as 50 bar or more, such as 60 bar or more,such as 70 bar or more, such as 80 bar or more, such as 100 bar or more,such as in the interval of 10-120 bar, such as in the interval of 50-120bar, such as in the interval of 80-120 bar. Then, an element may beprovided preventing the second and first parts from disengaging andreleasing the air pressure.

Presently, it is desired that the sealing allows a pressure of 60 bar,such as 80 bar, such as 100 bar may be maintained in the actuator for atleast 2 hours, such as 12 hours, such as 1 day, such as 2 days, such as4 days, such as 5 days.

The actuator may comprise a valve for introducing air into or removingair from the compartment as well as safety or overpressure valves or thelike.

The compartment is defined by a portion of the channel, such as aportion of the channel delimited by the second portion. The compartmentmay, naturally, extend also into the second portion. Thus, the “piston”may be hollow or itself have a channel extending in the same directionor along the same axis as the channel of the first portion.

When the second and first portions move in relation to each other, thesize and volume of the compartment changes.

A lubricating element is provided having one or more channels whichextend from the first to the second sides, so that air or gas may travelfrom one portion of the compartment defined partly by the first surface,through the lubricating element and to another portion of thecompartment defined partly by the second surface. The channels mayextend generally along a longitudinal direction of the compartment(direction of relative movement of the first portion in relation to thesecond portion) but may be meandering inside the lubricating element.The size, number and degree of meandering of the channels may beselected, as these parameters will define how much air/gas can penetratethe lubricating element per unit of time. If a swift action is desiredof the actuator, this amount of air/gas may be desired rather high.

The lubricating element is provided in the compartment and divides thecompartment into two end volumes each defined on either side of thelubricating element and along the direction of the compartment.

The lubricating element may be a monolithic or single element, such asif made of a solid element of plastics, polymer, metal, alloy, compositeelement or the like. The channels may be inherent in the material, suchas if the material is made from compressed, such as sintered, powder, ormay be made in the material, such as by drilling or the like.

Alternatively, the lubricating element may be made from a number ofelements, such as a large number of fibres which are interconnected,such as glued, adhered or sintered, to form a porous element.

When the first portion moves in relation to the second portion, not onlydoes the overall volume of the compartment change, also the volumes ofthe end volumes change. Thus, air or gas flow takes place between theend volumes through the lubricating element.

In one embodiment, the lubricating element seals or at leastsubstantially seals the compartment so that air/gas flow from one endvolume to the other takes place via the channels. To this effect, asealing element may be provided. In another embodiment, one or morelarger openings may be provided in the lubricating element to allow ahigher gas/air flow there through in order to increase the speed withwhich the actuator may act.

Any number of channels may be used, such as 1, 2, 5, 8, 10, 20, 30 ormore. In an element of sintered or compressed powder or fibres, thenumber may be much higher, often thousands.

In one element, the lubricating element is made of two elements: aventing element comprising one or more air ducts extending generally ina longitudinal direction of the compartment and

-   -   a porous element comprising the lubricant,        wherein, the porous element is positioned adjacent to openings        of the air ducts and closer to the end portion than the venting        element.

The porous element may have a thickness of at least ½ mm, such as atleast 1 mm, such as at least 2 mm. A diameter of the porous element maybe chosen as desired, such as 1-10 cm, such as 1-8 cm, such as 1-5 cm.

Any type of material may be used for the lubricating element, theventing element and/or the porous element, such as aluminum, carbon,carbon fibers, steel, stainless steel, titanium or more complexmaterials, such as chromed materials or combination of such material.Naturally, the strength and weight may be taken into account in additionto e.g. surface properties. Chromed surfaces, for example, may bedesired for providing wear resistant surfaces.

Then, the channels are formed partly by the ducts and partly by theporosity. Preferably, the ducts extend generally in a longitudinaldirection of the compartment.

The porous element, which has an open porosity, is positioned adjacentlyto openings of the air ducts and, as it is porous, also has therein airducts or passages, interconnected voids, pores, or channels to allow airflow there through from the venting element to the end volume adjacentto the porous element. The porous element preferably has a large numberof air ducts or openings, so that air received from the air ducts may bedistributed in the porous element and be output from a large number ofopenings. A porous element may be made of e.g. compressed powder, cork,sponge, pumice stone, a weave, non-woven, or similar, such as felt,fleece or the like.

The porous element may abut the venting element such as if attached tothe venting element in order to ensure that the air flow from the airducts enters the porous element.

The thickness and width of the porous element will depend on theporosity, the type and e.g. flow characteristics of the lubricant etc.

The lubricating element comprises a lubricant. The lubricant may be aliquid lubricant or a powder lubricant. An air flow through the channelswill force at least a part of the lubricant out of the channels, such asthe porous element, and into the end volume adjacent to the lubricatingelement, This lubricant may simply flow out of the lubricating elementor may, if the air flow is sufficiently high, be emitted as a lubricantmist which may settle on inner surfaces of the first and/or secondportions defining the end volume adjacent to the lubricating element.

When the lubricating element is close to the end portion, air flow intoand through the lubricating element will output lubricant also towardthe end portion and thus to an interface between the first channel andthe second portion and/or area where the first and second portions touchor engage. When the lubricating element comprises a porous element, thiselement preferably is closer to the end portion than the ventingelement.

An air flow through the lubricating element is obtained when therelative volume changes of the two end volumes differ. For example, ifone end volume, when the compartment is reduced in volume, is reduced to50% of its initial volume, and the other end volume is reduced to 90% ofits initial volume, the gas pressure in the first end volume is largerthan that in the other end volume—causing an air/gas flow.

The lubricating porous element may move in relation to any of or both ofthe first and second portions.

In one embodiment, the lubricating element is fixed, directly orindirectly, to the first portion. Thus, the lubricating element willmove in relation to the second portion, when the second portion is movedin relation to the first portion. This attachment may be a directattachment to a portion of the channel which the second element does notengage during normal operation.

In another embodiment, the lubricating element is fixed to the secondportion. The second portion, or a part thereof, moves inside thechannel, so that a fastening to the second portion is rather simple,such as a fastening to or inside a channel, if provided, of the secondportion.

An elongated element may be attached to an end of the elongatecompartment, and thus to one of the first and second portions, and tothe lubricating element.

It is noted that the total volume of an end volume need not be directlydefined by that of a portion of the compartment. The overall volume ofthe compartment may be determined by other parameters such as maximumdiameter/volume thereof as well as the maximum desired translation ofthe first portion in relation to the second portion. One or both of thefirst and second portions may have additional air/gas reservoirs influid connection with the inside of the compartment. Preferably, suchconnection is at the end of a first/second portion the farthest from theother of the first/second portion so as to not affect the translation ofthe first portion in relation to the second portion.

In this manner, the flow connection between the compartment and anair/gas reservoir clearly may also affect the operation of the actuator,as the amount of gas/air which can pass from the reservoir to thecompartment or vice versa per unit of time may be set to determine anoverall operation of the actuator.

Naturally, the volumes of the end volumes will change when the actuatoris compressed or extended. However, it may be desired that one endvolume is no less than 5 times, such as no less than 7 times, such as noless than 10 times the other end volume. Also, if the larger end volumecomprises a gas/air reservoir, it is desired that a flow connection fromthe reservoir to the compartment has a cross section of no less than 5%,such as no less than 10%, of a cross section of the compartmentperpendicular to the longitudinal axis and in that end volume. In thismanner, there will be no significant delay in pressure equalizationbetween that portion of the compartment and the reservoir. Clearly, adelay may be desired, such as if the actuation is desired slower. Such adelay may be obtained by a more narrow or longer flow connection betweenthe reservoir and compartment.

Another aspect of the invention relates to a method of operating theactuator according to the first aspect of the invention, the methodcomprising:

-   -   translating the second portion, in relation to the first        portion, from a first position to a second position in a first        direction along the longitudinal direction,    -   translating the second portion, in relation to the first        portion, from the second position to the first position in a        second, opposite direction along the longitudinal direction.

This translation may be a compression or an extension of the actuator bymoving the second portion further into or out of the channel in thefirst portion.

In one situation, a velocity of the movement in the first direction ishigher than a velocity of the movement in the second direction. This maybe the situation if, e.g., the actuator is energized or biased to beready to release the collected energy at a later point in time, such asfast as possible. Below, a bow incorporating such actuators isillustrated, where the actuator is biased in one direction by thepulling of the string and is allowed to release this energy, when thestring is released.

In fact, the actuator may be naturally biased toward one of thedirections, such as by providing therein an over pressure (actuatorbiased toward expansion) or a reduced pressure (actuator biased towardcontraction), where the faster movement then may be in the direction ofthe natural bias.

Preferably, a gas flows through the lubricating element during at leastone of the translating steps, such as during both translating steps.

Preferably, the gas flow caused by the higher velocity is a gas flowthrough the lubricating element, such as from the venting element towardand through the porous element. This velocity, together with parametersof the gas flow, the lubricating element and the lubricant may be sothat a lubricant mist is emitted into the end volume at the lubricatingelement.

The actuator may be used as a shock absorber. Thus, the flow through thelubricating element may be adapted to this use. The flow may be desiredlower when acting as a shock absorber than when used for receiving andexerting a force such as when used in a bow. Also, the volumes below andabove the lubricating element may be selected, as the pressure increaseupon compression and the amount of air/gas transported through thelubricating element may be chosen differently in the two situations.

A third aspect of the invention relates to a bow having a first andsecond extreme portions and a double string comprising:

-   -   a first string having a first end, a second end and a central        portion,    -   a second string having a first end, a second end and a central        portion and    -   an interconnecting element,        wherein    -   the first and second ends of the first string are attached to        the first extreme portion,    -   the first and second ends of the second string are attached to        the second extreme portion and    -   the interconnecting element is slidably attached to the central        portions of the first and second strings.

A bow may be any type of bow, such as a long bow a recurve bow, acompound bow, a cross bow or the like, where an arrow, bolt or similarelongate projectile is launched by a string biased in the oppositedirection of the launch direction.

The extreme portions of a bow usually are the outer, opposite portionsthereof. Such portions may have means for engaging the string, such asgrooves or holes. Some bows have more intricate elements, such as camshaving therein grooves for receiving and controlling the string.

The present string is formed by two strings each having a first and asecond end and a central portion. The central portion is positionedbetween the ends but not necessarily directly centered between these.

The ends of the strings are attached to the extreme portions. Naturally,the strings may be longer, so that portions thereof extend away from theextreme portions. For example, in compound bows, the string will extendover the cam of one limb and back toward the other limb. However,functionally, the ends are those contacting the extreme portions.

The interconnecting element is slidably connected to the strings, sothat each string may have a U-shape having the legs toward thepertaining extreme portion and the interconnecting element at thebottom. Then, one portion of a string (one leg of the U) is looser thanthe other, the slidable engagement will allow the two portions to obtainthe same tension.

This is the situation for both strings and thus for all portions of thestrings between the two extreme portions.

The slidable connection or attachment may be obtained having a stringextend through a simple hole or channel in the interconnecting element.Thus, the interconnecting element may comprise at least one hole throughwhich a central portion of the first or second string extends.

More intricate manners may be used where the string engages a rotatablewheel of the interconnecting element.

An advantage of the double string is that the string is less prone tosideward movement when launching an arrow.

In one embodiment, the first and second extreme portions each comprisesa rotatable cam, wherein both the first and the second ends of bothstrings engage the extreme portions of the bow via the cams, the camshaving double grooves configured to accept the ends of the strings. Suchcams often are rotatably attached to the remainder of the bow, such asspring biased in one direction opposite to the direction of rotationcaused by drawing of the string away from a handle portion of the bow.

In one embodiment, the interconnecting element is at least generally U-or V-shaped having two legs and a center part, engages each of thecentral portions at a respective leg and has means for engagement of anarrow at the center part.

Naturally, this aspect of the invention may be combined with any of theother aspects, embodiments and features of the invention, as may theother aspects/embodiments and features.

Another aspect of the invention relates to a bow comprising a frame anda string, the string being connected to the frame via two cams beingpositioned at opposite ends of the frame, the frame comprising:

a central portion having two extreme portions,

a first portion and a second portion, each portion having a first endand a second end, each portion being rotatably attached, at its firstend, to or at an extreme portion of the central portion, each of thecams being attached to or at the second end of one of the first andsecond portions of the frame,

at least two pneumatic actuators, of which one is positioned between thecentral and first portion, and another one is positioned between thecentral and second portion.

Again, a bow may be any type of product or instrument useful forlaunching a projectile, such as an elongate arrow/bolt or the like bypulling the string in the opposite direction and allowing the string tolaunch the arrow/bolt when it is released.

The bow has a central portion and two portions to which the cams areattached. The portions are rotatably attached to the central portion,and each portion has an actuator.

The actuator preferably is an actuator which may be compressed orextended and which therein has a compartment with an air pressureincreasing or decreasing due to the compression/extension and which mayexert an opposite movement or force when allowed to do so. This actuatormay be that according to the first aspect of the invention.

The actuators preferably are attached to the central portion and thefirst/second portion and are affected when the pertaining portion isrotated in relation to the central portion. Preferably, the actuator isnaturally biased in a direction where the first/second portion isrotated away from the string and/or in a manner so as to tension thestring.

In one embodiment, the pneumatic actuators are configured to beenergized (such as when compressed or extended) when the respectiveportion is rotated, in relation to the central portion, in a directiontoward the string, such as when the string is pulled away from thecentral portion. This received energy may then be output to cause arotation in the opposite direction.

In one embodiment, each actuator is connected to its respectivefirst/second portion at a position between an axis of rotation betweenthe respective portion and the central portion and a position ofattachment of the respective portion and its cam. In this manner, themovement caused by the actuator is amplified due to the difference indistance from the point of rotation to the point of engagement of theactuator and the distance from the point of rotation to the point ofengagement of the string. This difference in distance may be seen as agearing of the movement of the actuator to the movement of the cam andthus the string.

In one embodiment, the central portion comprises a first and a secondintermediate element and a central element having two outer ends, eachintermediate element being connected, at one end thereof, to an outerend of the central element and, at its other end, rotationally connectedto a respective first/second portion, the actuators being connected to arespective intermediate element, where the intermediate elements aredetachably attached to the central portion.

When each intermediate element is rotatably connected to one of thefirst/second portions and the actuator is connected to these elements,this assembly, which may be called a limb of the bow, may be removedaltogether from the central element. The bow thus may be reduced in sizeand more easily transported. Also, such limbs may then be re-used orattached to another type of central element, such as an element havingother dimensions or other capabilities (having other aiming instruments,other handles or the like). In fact, the same limbs may be used both ona compound bow and a cross bow.

In addition, the limbs may be locked in an actuated position, such as ina position in which the actuators are compressed so that the distancebetween the cams is reduced. In this manner, the string may be easilyremoved and replaced. This locking may be a locking of the relativeintermediate element and extreme element in the desired angle.

Assembly of the bow may then be the re-attachment of the limbs to thecentral element and the re-placing of the string, where after thelocking of the limbs is removed, preparing the bow for action. Thelocking may simply be achieved by bringing the limbs to the desiredangle, such as by pulling the string of the bow, where after a bolt ispositioned in corresponding holes of the elements of the limbs lockingthe limbs in that angle. The removal of the locking may then be, afterattaching the limbs to the central element, pulling the string torelieve the tension on the bolts which may then be removed such as byorientating the bow in the horizontal plane so that the bolts drop outof the holes by the action of gravity.

In general, when two actuators are used in a bow, it is desired toensure that both actuators exert the same force on the string. This maybe obtained by supplying pressurized air to both actuators, such asusing a T-shaped tube from a pump to the two actuators.

A final aspect of the invention relates to a bow comprising:

-   -   a central portion having two extreme portions,    -   first and second inner elements each having a first and a second        end, each of the first ends being rotatably connected to an        extreme portion of the central portion,    -   first and second outer elements each having a first and a second        end, each of the first ends of the outer elements being        rotatably connected to a second end of the inner elements,    -   a first and a second actuator, the first actuator acting between        the central portion and the first outer element, at a first        position thereof between the ends thereof, and the second        actuator acting between the central portion and the second outer        element, at a second position thereof between the ends thereof,    -   a first and a second non-extendable element the first        non-extendable element acting between the central portion and        the first outer element, at a third position between the ends of        the first outer element and being different from the first        position, and the second non-extendable element acting between        the central portion and the second outer element, at a fourth        position between the ends of the second outer element and being        different from the second position.    -   a string extending between the second ends of the outer        elements.

Again, the above bow definition would be suitable in this respect.

The inner elements are rotatably connected at one end to the centralportion and at the other end to the outer elements. The string extendsbetween the second ends of the outer elements. Naturally, cams or thelike may be provided at the second ends of the outer elements to arriveat e.g. a compound bow.

The actuators may be of any type, such as springs, pneumatic actuators,hydraulic actuators or the like. Preferably, the actuators are of thetype according to the first aspect of the invention.

Each actuator is connected to the central portion and the pertainingouter element. The actuator acts on the outer element at a firstposition or second position, respectively, thereof between the endsthereof.

A non-extendable element is an element which is not extended to anysignificant degree by the action of the actuator and/or the normaloperation of the bow. Thus, the non-extendable element defines andmaintains a predetermined distance between the central portion and thepertaining outer element, or rather the positions or portions thereof towhich the non-extendable element is attached. This attachment preferablyis a rotational attachment.

The non-extendable element may be a stiff element, such as a metalelement (such as a rod), a wire or the like.

The non-extendable elements engage the outer elements at the third andfourth position, respectively, which are different from the first/secondpositions. When the outer elements are engaged at different positions,such as different longitudinal positions between their ends, the actionof the actuator will affect a movement, such as a rotation or a morecomplex movement, of the second end and thus the string, due to theaction of the non-extendable element.

Preferably, the first and second positions correspond to each other,such as with the same distance from one end or both ends of the outerelements. Preferably, the third and fourth positions are corresponding,such as with the same distance from one end or both ends of the outerelements.

In one embodiment, the third and fourth positions are closer to thefirst ends of the outer elements than the first/second positions. Thus,a gearing may be seen where the movement caused by the actuator and thatseen at the second ends of the outer elements.

In one embodiment, two cams are provided and positioned one at eachsecond end of the outer elements, the string extending between the cams.Thus, the bow may be a compound bow.

In one embodiment, the central portion comprises a first and a secondintermediate element and a central element having two outer ends, eachintermediate element being connected at one end thereof to an outer endof the central element and, at its other end, rotationally connected toone of the inner portions, the and non-extendable elements and actuatorsbeing connected to a respective intermediate element, where theintermediate elements are detachably attached to the central portion.Thus, the assemblies of the intermediate, inner and outer elements andfurther comprising the actuators and non-extendible elements, suchassemblies may be called limbs of the bow, may be detached from thecentral element, so that the bow may be reduced in dimensions and thusmore easily transported.

In a particularly interesting embodiment, the bow further comprises alocking element for locking the first inner element in a predeterminedrotational position in relation to the first outer element. In thismanner, the actuator may be locked in a biased state so that the stringmay be replaced or, in the above situation, the limbs may be removed ina state where the string is not tensioned.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, preferred embodiments of the drawings will bedescribed, wherein:

FIG. 1 illustrates a pneumatic actuator,

FIG. 2 illustrates a double string for a compound bow,

FIG. 3 illustrates a compound bow, and

FIG. 4 illustrates a first embodiment of a limb of a compound bow.

DETAILED DESCRIPTION

FIG. 1 illustrates a pneumatic actuator 100. The actuator comprises afirst portion 101 and a second portion 102. The first portion 101defines a closed first channel 1011 while the second portion 102 has apart 1021 being slidably positioned in the first channel 1011 of thefirst portion. The part 1021 of the second portion has an end portion1022 which slides along the first channel 1011. The actuator furthercomprises a venting element 103 comprising one or more air ducts 104.The venting element may be either stationary element or it may slidealong the channel of the first portion or inside a second channel 1023of the second portion 102. FIG. 1 illustrates the venting element withits major part positioned within the second channel 1023.

Only a part of the venting element is within the first channel. Aremainder of the venting element is in the second channel. The air ducts104 are extending generally in a direction of the channels. The airducts extend along the longitudinal direction of the entire ventingelement. Above the venting element 103 is a porous element 105comprising a lubricant. A porous element may be a material withinterconnected voids, pores, or channels, such as a compressed powder,cork, sponge, pumice stone, a weave, non-woven, or similar, such asfelt, fleece or the like.

As the porous element 105 is positioned adjacently to openings of theair ducts, and closer to the end portion 1022 than the venting element103, air passing through the air ducts will also pass through the porouselement and cause at least a part of the lubricant to be forced out ofthe porous element, such as a lubricant mist, to lubricate the walls ofthe channel of the first portion and thus an interface between the firstand second portions. The pneumatic actuator further comprises a guidepin 106 which may serve as a fixture of the actuator 100 to anotherelement. The actuator 100 can be disassembled and the guide pin 106 canlimit the movements of the first and second portion during disassembly.The bottom part of the actuator has a safety valve port 107 and a loadvalve port 108. A loop 109 is provided for fixing another element to theactuator opposite to one connected the guide pin 106.

The operation of the lubrication of the actuator is that duringcompression, an upper volume above (in the drawing) the venting elementand porous element will change, as will a lower volume below the ventingelement. Thus, air transport through the venting element/porous elementis required to equal the pressures in the two volumes.

The same will be the situation when the actuator is again extended, suchas released, so that the volumes normalize. Naturally, the actuator maybe used equally well for initial extension (generate vacuum or a lowerpressure) or an initial compression (increase pressure therein).

The air transport through the venting element and porous element thuswill affect the lubricant in the porous element. Preferably, the airtransport in a direction from the venting element toward the porouselement is higher than that in the opposite direction, so that theoverall lubricant transport is out of the porous element and into theupper chamber in the drawing.

Thus, the venting element and porous element may move, relative to thefirst and/or second portion, during compression/expansion.Alternatively, they may be fixed to one of the first or second portions.

Preferably, the porous element is positioned closer to the end portion1022 when the lubricant is emitted, so that the lubricant accesses theinterface between the first and second portions.

Therefore, the venting element may, in the drawing, be positioned overthe porous element, if these are then provided higher than the endportion 1022.

Naturally, the size of the volumes above and below the venting elementand porous element may be adapted by adapting the first and secondportions as may the interface between the first and second portions sothat the volume change above and below the venting element and porouselement are as desired.

The position of the venting element and porous element may be selectedfrom the expected velocity of the expansion/compression. Preferably, oneof the expansion and compression takes place faster than the other, sothat the air or gas transport through the venting element is faster inone direction than the other. Preferably, the porous element ispositioned at the end of the venting element outputting the air/gas withthe higher velocity, as this has the best opportunity to generate alubricant mist.

The lubricant preferably is a liquid or fluid with flow characteristicsallowing it to enter the porous material. Thus, the porous materialpreferably is of a type having openings/pores and surfacecharacteristics allowing the lubricant to enter into the porousmaterial.

Alternatively, the porous material and lubricant may be selected so thatthe lubricant does not enter or does not to any significant degree enterthe porous element. This may be due to the lubricant having a lowviscosity or a large particle size and/or the porous element havingsmall openings at its upper side or being made of a material repellingthe lubricant. In this situation, it is preferred that the lubricantdoes not travel through the porous material and into the ventingelement.

Clearly, the venting element and porous element may be replaced by asingle element having an open porosity or channels therein.

Also illustrated is a air/gas reservoir 1030 connected via a flowconnection to the end volume above the porous element 5, thuseffectively increasing that volume without changing the overall relativeproperties of the first and second portions. The volume of the reservoirand the size of the flow channel will take part in the definition of theflow inside the actuator upon compression or expansion.

FIG. 2 illustrates a double string for a bow. FIG. 2 a illustrates afront view of the double string configuration while FIG. 2 b illustratesa side view of the double string provided on a cam as is usual incompound bows. The double string comprises a first string 201, a secondstring 202 and an interconnecting element 203. The interconnectingelement may be made of aluminium, metal, alloy, plastics, polymers,steel, leather or similar. Only a part of the second string isillustrated in both FIGS. 2 a and 2 b . However, it is preferablysymmetrical to the first string. The interconnecting element 203 has anupper portion 203 a and a lower portion 203 b. The central portion ofthe first string 201 a is slidably connected to the upper portion 203 aof the interconnecting element and the central portion of the secondstring is connected to the lower portion 203 b of the interconnectingelement. Free ends of the first string, 201 b and 201 c, are connectedto the bow, such as the cams of a compound bow.

When used with a compound bow, the double string could be received indouble grooves in the cams.

The advantage of the double string is two-fold. Firstly, the twoparallel strings will counter-act sideward movement (in FIG. 2 a ) ofthe string during launching of an arrow.

The dividing of the double string using the slidable connection of theinterconnecting element allows the two strings (the four half-strings)to be equally tensioned. If, e.g. (FIG. 2 a ) the right string was moreloose than the left string, the strings would rotate during launching ofthe arrow, naturally affecting the delivery and flight of the arrow.

The slidable connection may be a simple hole through which thepertaining string extends and is allowed to slide along the string.Naturally, a more complex solution may be chosen where the stringextends on a wheel, cam or the like rotatably connected to theinterconnecting element.

The interconnecting element may be V-shaped so that the strings may beconnected to the arms and an archer may engage the interconnectingelement at the bottom of the V. An arrow may be engaged by an elementextending inside the V-shape.

A double string may be used on any type of bow, long bows, recurve bows,compound bows, cross bows or the like.

FIG. 3 illustrates a compound bow 300. The bow comprises a frame 301 anda bow string 302. The bow string 302 is connected to the frame via twocams 303 a and 303 b which are positioned at ends of the frame 301. Theframe comprises a central element 304, a first limb 305 and a secondlimb 306. The first and second limbs are preferably detachably attachedto the central element 304. Alternatively, a central portion may beformed by the central element and the intermediate parts also.

The cams 303 a and 303 b are attached to the outer ends of the first andsecond limbs. The cams have grooves configured to accept the bow string302.

Each limb has an intermediate part 305 a and an outer part 305 brotatably attached to each other. The intermediate part is detachably orpermanently attached to the central portion and the outer part isrotatably attached to one of the cams.

The frame further comprises two pneumatic actuators 307 a and 307 b,each being positioned between the intermediate and outer parts of alimb. The actuators may be of the type illustrated in relation to FIG. 1. However, also other types of actuators, such as springs, hydraulicactuators or the like may be used.

Clearly, when the string 302 is pulled back, the cams are rotated andthe outer parts rotated in relation to the intermediate parts, thuscompressing the actuators.

In addition to the spring tensioning of the cams and thus releasethereof when they are allowed to rotate back to their initial rotationalpositions, when the string is released, the actuators will act to rotatethe intermediate/outer parts of the limbs back to the initial positions.It is seen that an even larger effect is achieved due to the “gearing”obtained due to the distance between, on the one hand, the axis ofrotation between the intermediate and outer parts and the point ofattachment of the actuator on the outer part and, on the other hand, thepoint of attachment of the actuator on the outer part and the positionof engagement of the string and the cam.

It may be desired to be able to dis-assemble the bow, such as when theintermediate parts and the central element may be detached from eachother or if the string is desired removed/replaced. Thus, it may bedesired to be able to lock the actuator in a compressed state. Manymanners of obtaining this exist, such as providing the actual actuatorwith a system preventing it from expanding from a compressed position.Preferably, an element is provided for locking the intermediate part ina desired angle in relation to the outer part. This may be a simple boltextending through corresponding holes in the intermediate part and theouter part, when the angle is provided. Providing the angle may simplybe pulling the string. Having obtained the angle, the bolts may beinserted, where after the string may be relaxed or even removed and thelimbs may be detached from the central element. Re-attachment is simple,and the bow may then be made operational by again pulling the string,relaxing the forces acting on the bolts which may then be removed.

In one embodiment, seen in FIG. 4 , an inner element 305 c is providedbetween the intermediary part 305 a and the outer part 305 b. The innerelement 305 c is rotationally connected to each of the intermediary part305 a and the outer part 305 b.

In addition, a non-extendable element 305 d, such as a wire, rope, rodor the like, is provided between the outer part and the intermediarypart. The actuator 307 a is attached to the outer part at a positionbetween the attachment positions of the cam 303 a and the non-extendablepart, respectively. In this embodiment, the actuator is attached to theouter part at the rotational connection between the outer part and theinner part. This, however, is not a requirement.

It is seen that now the “gearing” of the cam axis or the point ofcontact between the string and the cam, compared to the intermediaryportion, is defined by the relative positions of the attachmentpositions of the outer element to the actuator and the non-extendableelement, respectively.

In this situation, rotation may be locked between the outer part and theinner part, as this can lock the actuator in e.g. a compressed state.One manner of obtaining this rotational locking is to lock the outerpart to the inner part, such as at a position away from the rotationalattachment between these elements—such as at a position 305 e at the endof the outer part the farthest from the cam. Locking the outer part tothe inner part when the actuator is compressed would lock the inner,outer and intermediary parts and the actuator in a predeterminedconfiguration, where after this assembly may be disengaged from thecentral element if desired and/or the string may be removed. In fact,the limbs may be attached to e.g. another central element with othercapabilities, such as with another handle, other aiming means or to formanother type of bow, such as a cross bow.

The above aspects and technologies may be combined to form differenttypes of products, such bows, compound bows, recurve bows, long bows,cross bows or the like.

What is claimed is:
 1. A pneumatic actuator, comprising: a first portionand a second portion, the first portion defining a closed channel, thesecond portion having a part being slideably positioned in the channel,the part having an end portion positioned in the channel, the first andsecond portions defining an elongate compartment comprising at least aportion of the channel; a lubricating element provided in the channel,the lubricating element having: a first surface facing the firstportion; a second surface facing the second portion; one or morechannels extending from the first surface to the second surface; and alubricant in or on the lubricating element.
 2. The pneumatic actuatoraccording to claim 1, wherein the lubricating element is fixed inrelation to the first portion.
 3. The pneumatic actuator according toclaim 1, wherein the lubricating element is fixed in relation to thesecond portion.
 4. The pneumatic actuator of claim 1, wherein thelubricating element comprises: a venting element comprising one or moreair ducts forming part of the one or more channels; and a porous elementcomprising a lubricant, wherein, the porous element is positionedadjacently to openings of the air ducts and closer to the end portionthan the venting element.
 5. The pneumatic actuator according to claim4, further comprising an elongate element connecting the venting elementand porous element to the pertaining first or second portion.
 6. Amethod of operating the pneumatic actuator of claim 1, the methodcomprising: translating the second portion, in relation to the firstportion, from a first position to a second position in a first directionalong the longitudinal direction, and translating the second portion, inrelation to the first portion, from the second position to the firstposition in a second, opposite direction along the longitudinaldirection.
 7. The method according to claim 6, wherein a velocity of themovement in the first direction is higher than a velocity of themovement in the second direction.
 8. The method according to claim 6,wherein a gas flows through the venting element and the porous elementduring at least one of the translating steps.
 9. A bow comprising aframe and a string, the string being connected to the frame via two camsbeing positioned at opposite ends of the frame, the frame comprising: acentral portion having two extreme portions; a first portion and asecond portion, each of the first and second portions having a first endand a second end, each of the first and second portions being rotatablyattached, at its first end, to or at an extreme portion of the centralportion, each of the cams being attached to or at the second end of oneof the first and second portions of the frame; and at least twopneumatic actuators, of which one is positioned between the central andfirst portion, and another one is positioned between the central andsecond portion.
 10. The bow according to claim 9, wherein the pneumaticactuators are configured to be energized when the respective portion isrotated, in relation to the central portion, in a direction toward thestring.
 11. The bow according to claim 9, wherein each actuator isconnected to its respective first or second portion at a positionbetween an axis of rotation between the respective first or secondportion and the central portion and a position of attachment of therespective first or second portion and its cam.
 12. The bow according toclaim 9, wherein the central portion comprises a first and a secondintermediate element and a central element having two outer ends, eachintermediate element being connected at one end thereof to an outer endof the central element and, at its other end, rotationally connected toa respective first or second portion, the actuators being connected to arespective intermediate element, wherein the intermediate elements aredetachably attached to the central portion.
 13. The bow according toclaim 9, further comprising locking means configured to fix the firstintermediate element in a predetermined angle to the first portion andthe second intermediate element in a predetermined angle to the secondportion.